Remove redundant plugin initialization

Patch from Justin Azoff to remove a redundant plugin initialization (as a
result of this bug, exceptions were not being caught).
Use getattr for looking up plugin methods

Patch from Justin Azoff to simplify plugin code.  This patch changes
the previous behavior slightly because instead of only calling the
cmd_XXX_pre/post functions for plugins that override the base class
function, now we always call the function (the base class function
is always just a noop, so this doesn't produce any side effects).
Also, in the event of a future bug in broctl where the getattr lookup
fails, then broctl will now terminate with a Python stack trace
instead of silently ignoring the problem.
Enable dead hosts caching while in cron mode

Patch from Justin Azoff to enable dead hosts caching while in cron mode.
Fix plugin init return values

The myricom plugin wasn't explicitly returning a value from its init
method, so it was being disabled as a result.  Fixed return values
in the init method in the myricom and pf_ring plugins.  Also added a
debug message when a plugin is disabled so that this issue is easier
to diagnose in the future.
Improve broctl output formatting

Increased width of node name column in the status, top, df and print
command output in order to ensure column alignment when longer node names
(such as "worker-1-10") are in use.  Decreased width of some columns in
the top command output in order to keep the line length less than 80.
Increased length of the divider line in the capstats output.
Fix broctl top on OS X Mavericks

The top command output changed in OS X Mavericks, which was breaking
the broctl top command (the column numbers that the top helper script
needs to use are different in Mavericks).  Also noticed that the grep
command used by the broctl top helper script was not completely
filtering out the first sample output of top (because there are
multiple launchd processes).  Fixed both issues (should also work
on older versions of OS X).
Fix redundant emails from broctl cron when dead host found

A recent commit ("Enable dead hosts caching while in cron mode"),
had the side effect of generating redundant email messages when
broctl cron detected a dead host.  The fix is to output the warning
message only when not in cron mode (broctl cron has its own
mechanism for reporting dead hosts).
Improve broctl output formatting

Increased width of the hostname column in the output of the broctl
status, top, and capstats commands in order to improve readability.
Also removed some trailing spaces in order to keep the line length
less than 80.
Move debug output to the debug.log

Moved some debug output that occurs only when a node is slow to
start or stop to the debug.log file and added an explanation in the
message.
Merge remote-tracking branch 'origin/master' into topic/dnthayer/misc-improvements
Merge remote-tracking branch 'origin/fastpath'

* origin/fastpath:
  Fix bug with IPv6Comm broctl option
Merge remote-tracking branch 'origin/topic/dnthayer/misc-improvements'

BIT-1112 #merged

* origin/topic/dnthayer/misc-improvements:
  Move debug output to the debug.log
  Improve broctl output formatting
  Fix redundant emails from broctl cron when dead host found
  Fix broctl top on OS X Mavericks
  Improve broctl output formatting
  Fix plugin init return values
  Enable dead hosts caching while in cron mode
  Use getattr for looking up plugin methods
  Remove redundant plugin initialization
Correct typo in CHANGES and update the docs

Did a "make doc" to update the docs.